The single, brick-and-mortar, structure is perfectly square with no windows. On the east side, a complete Buddha image sits in a position of meditation. This image is framed by the backdrop of a large bodhi tree, which has grown over a large portion of the water tank. This structure is sometimes mistaken for a mondop due to the Buddha image; however, it was build for the exclusive purpose of water storage. It has been renovated by the Fine Arts Department.

Charnvit Kasetsiri & Michael Wright point out that the Royal Palace had an elaborate irrigation system - including bronze and terracotta water pipes, plumbing trenches, and water wheels (p 326-327). Some of the ancient irrigation system, such as water pipes, can still be seen at Wat Phra Si Sanphet. An ancient pool can also be seen close to water tank. Records show that a second water tank was once located inside the inner palace.

(The water tank is visible under left)Williams-Hunt Aerial Photos Collection. Original from the School of Oriental and African Studies (SOAS), University of London. Digital Data from Center for Southeast Asia Studies (CSEAS), Kyoto University. Digital Archive from Chulachomklao Royal Military Academy (CRMA), Thailand